An explosion on the Deepwater Horizon rig at BP's Macondo undersea well in the Gulf of Mexico on April 20, 2010 killed 11 workers and spewed nearly 5 million barrels of oil into the sea, triggering the largest offshore oil spill in U.S. history.

Initially when the rig exploded and sank in the Gulf of Mexico, off the coast of Louisiana, authorities denied of any leakage of crude oil into the ocean. However, oil deposits washed up on the shores told a different tale.

An expedition to the bottom of the Gulf of Mexico this February revealed that last April oil spill from the UK energy giant's ruptured well will take months or even years to clean up, according to marine scientists.

More recently, over 400 dolphins were reported to have washed up dead on the Gulf Coast in the last three months, raising thougths over BP's oil spill to be the possible cause for their death.

While the spill badly hit tourism in the region, affecting the coastal economies of Florida, Mississippi, Alabama and especially Louisiana, oil gushed into the sea one year back, continues to clog wetlands, pollute the ocean and endanger wildlife despite various restoration projects running along the shores.

Below are some of the latest pictures taken on April 20, 2011, exactly one year after the environmental disaster hit the regions of Gulf of Mexico:

A white Fiat van rammed into pedestrians outside enjoying a late afternoon stroll on Las Ramblas in Barcelona on Thursday killing at least 13 people and leaving hundreds injured. The Islamic State group claimed responsibility for the attack.